fix!(core): Make HubSwitchGuard !Send to prevent thread corruption #957
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Jan 14, 2026
HubSwitchGuard manages thread-local hub state but was Send, allowing it to be moved to another thread. When dropped on the wrong thread, it would corrupt that thread's hub state instead of restoring the original thread. To fix this, add PhantomData<MutexGuard<'static, ()>> to make the guard !Send while keeping it Sync. This prevents the guard from being moved across threads at compile time. Additionally, refactor sentry-tracing to store guards in thread-local storage keyed by span ID instead of in span extensions. This fixes a related bug where multiple threads entering the same span would clobber each other's guards. Fixes #943 Fixes #946 Refs RUST-130 Refs RUST-132 Co-Authored-By: Claude <noreply@anthropic.com>
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Description
HubSwitchGuardmanages thread-local hub state but wasSend, allowing it to be moved to another thread. When dropped on the wrong thread, it could corrupt that thread's hub state instead of restoring the original thread.This PR makes
HubSwitchGuard!Sendby addingPhantomData<MutexGuard<'static, ()>>while keeping itSync. The type system now prevents the guard from being moved across threads at compile time.To ensure guards are always dropped on the originating thread,
sentry-tracingnow stores them in thread-local storage keyed by span ID rather than in span extensions.Issues